The present invention generally relates to an optical apparatus which is constituted by a main optical body and an auxiliary optical device mountable on and dismountable from each other, and more particularly, to a positioning mechanism of the optical apparatus for positioning the auxiliary optical device relative to the main optical device in the mounting completed condition and further to the auxiliary optical device which has a positioning recess constituting a part of the positioning or locking mechanism.
A typical example of this kind of optical apparatuses is a lens interchangeable camera constituted by a camera body as the main optical device and an interchangeable lens as the auxiliary optical device. Conventional mounting and dismounting mechanisms provided on this kind of optical apparatuses have already minimized a mounting torque and a rotational angle necessary for the mounting of the auxiliary device on the main device, so that rapid mounting and dismounting operations are made possible when desired. For example, in the case of a lens interchangeable camera as described above, a photographer can replace an interchangeable lens mounted on a camera body with another one instantaneously in accordance with his or her choice. However, rapid mounting and dismounting operations, when repeated, give rise to ill affections on the positioning mechanism of the optical apparatus as described later in detail.
A lens interchangeable camera as an example of such optical apparatuses equipped with a positioning mechanism is proposed in Japanese Utility Model Publication No. 50420/1978 (Jikkosho 53-50420). The camera is provided with a bayonet mounting mechanism. When a positioning member is displaced to such a predetermined position as to confront a positioning recess upon an operation for mounting the interchangeable lens on the camera body, the positioning member urged by a spring projects into the positioning recess so as to be brought into engagement with the positioning recess. Meanwhile, the positioning member is disengaged from the positioning recess upon a disengagement operation of an unlocking member. However, in this known positioning mechanism, when the interchangeable lens is rapidly mounted on the camera body, the positioning member urged by the spring projects into the positioning recess at a speed lower than a rotational speed for mounting the interchangeable lens on the camera body and therefore, comes into collision with a rear side face of the positioning recess before projecting into the positioning recess to a predetermined depth, with the result that the engagement of the positioning member with the positioning recess is insufficient while the mounting operation for mounting the interchangeable lens on the camera body is completed. In the case where interchange of the interchangeable lens is performed frequently causing such insufficient engagement between the positioning member and the positioning recess, the rear side face of the positioning recess formed on the mount face of the interchangeable lens is gradually dented by large impact forces applied frequently thereto from the positioning member provided in the camera body and thus, the mount face of the interchangeable lens swells at the side face of the positioning recess. Meanwhile, the positioning member of the camera body is also gradually dented, at its portion brought into collision with the rear side face of the positioning recess, due to its insufficient engagement with the positioning recess. Consequently, a play between the positioning member and the positioning recess increases. Moreover, the positioning member, which is slidably fitted in a guide hole formed on a mount face of the camera body, is strained to come into accidential frictional contact with the peripheral face of the guide hole and thus fails to project into the positioning recess sufficiently. In an extreme case, such a phenomenon takes place that the mounting operation is completed without engagement between the positioning member and the positioning recess through skip of the positioning member over the positioning recess.
Recently transmission of electric signals and mechanical driving forces between a camera body and an interchangeable lens has become more and more necessary in lens interchangeable cameras to increase their performance such as automatic exposure control and automatic focus control. Here assume that a camera includes transmission members for transmission of various electrical signals and mechanical driving forces between a camera body and an interchangeable lens and that a known positioning mechanism as described above is employed to such a camera. If the mounting of the interchangeable lens on the camera body is completed with improper positioning of the interchangeable lens relative to the camera body due to increasement of the play between the positioning member and the positioning recess or due to skip of the positioning member over the positioning recess, the transmission members will fail to perform the electric signal and driving force transmission as required, resulting in, for example, erroneous exposure control and focus control. Particularly in case a driving force for automatic focus control is transmitted from a camera body to an interchangeable lens through a driving shaft on the side of the camera body and a driven shaft on the side of the interchangeable lens and the driving shaft engages the driven shaft in association with the projection of the positioning member into the positioning recess, the improper positioning of the interchangeable lens relative to the camera body will result in an insufficient engagement between the driving and driven shafts, and therefore, engaging portions of the driving and driven shafts will be damaged when an automatic focusing operation to rotate the driving shaft is started by a photographer who is unaware of the improper positioning.
Another example of a lens interchangeable camera equipped with a positioning mechanism is proposed in Japanese Utility Model Publication No. 38911/1979 (Jikkosho 54-381911). The camera in this case is provided with a screw or thread mounting mechanism. A positioning member provided on a camera body is fitted into a positioning recess formed on the interchangeable lens during a final time rotation of the interchangeable lens for threadedly mounting the interchangeable lens in position. In this prior art camera, even if the interchangeable lens is erroneously threaded into the camera body after an unlocking member has been depressed, the interchangeable lens is fixed in position. Furthermore, since a gentle inclined face is so formed as to extend continuously from the positioning recess in the rotational direction for dismounting the interchangeable lens from the camera body, it becomes possible to threadedly disengage the interchangeable lens from the camera body by depressing the unlocking member. Namely, in this prior camera, since the gentle inclined face, whose angle of inclination will be preferably set to be not more than 45.degree. in view of demounting of the interchangeable lens from the camera body, is so provided as to extend continuously from the positioning recess in the rotational direction for dismounting the interchangeable lens from the camera body as described above, the positioning member projects into the positioning recess after slidingly contacting the gentle inclined face. Accordingly, in the case where the interchangeable lens is rapidly mounted on the camera body, the amount of the projection of the positioning member into the positioning recess becomes insufficient due to the small angle of inclination of the inclined face with a consequence that the positioning member will not be able to fully engage the positioning recess. This may cause the positioning member and the rear side face of the positioning recess to be dented by impact forces produced therebetween. Furthermore, if this prior art camera were constructed to effect drive transmission for focus control between the camera body and the interchangeable lens through driving and driven shafts brought into engagement with each other in operative association with the projection of the positioning member into the positioning recess, the problem of the damage of engaging portions of the driving and driven shafts would occur in the same manner as described earlier. In addition, upon dismounting of the interchangeable lens from the camera body, the driving shaft would be still held in slight engagement with the driven shaft while the positioning member would be retracted away from the positioning recess to a height corresponding to the inclined face so as to disengage from the positioning recess, so that such a problem might arise that a rotational force for dismounting the interchangeable lens from the camera body is received by the driving shaft but not by the positioning member thereby increasing the possibility of the damage of the engageable portions of the driving and driven shafts.
In U.S. Pat. No. 4,449,807, a lens interchangeable camera is proposed in which in the case where an automatic focusing driving shaft provided in a camera body is insufficiently engaged with a driven shaft provided in an interchangeable lens, a switch member is opened or closed by the driving shaft or a positioning member associated operatively with the driving shaft so as to generate a warning signal or so as to make the optical apparatus inoperative for notifying the operator of the necessity to secure a proper engagement between the driving shaft and the driven shaft. Thus, it is possible to prevent the positioning member or the positioning recess from being dented or eliminate inaccurate information transmission between the camera body and the interchangeable lens. However, this known optical apparatus suffers from rise in production cost since the switch member is provided and is required to be adjusted in position. Moreover, since an additional space is required for the switch member, the known optical apparatus is made large in size.